Thixotropic Behavior Research Articles

Pharmacotechnical aspects of a stable probiotic formulation toward multidrug-resistance antibacterial activity: design and quality control

As a well-known group of the probiotic family, the Lactobacillus has increasingly contributed to hindering the growth of pathogens, particularly resistant species, in the last decades. Since antibiotic resistance has become a severe problem in global healthcare systems and considerably increased the mortality and morbidity rate in infectious diseases, we aimed to obtain a new stable formulation of Lactobacillus to overcome resistant infections. For this purpose, we designed various gel formulations containing Lactobacillus rhamnosus (L. rhamnosus) as an active pharmaceutical ingredient (API) in a water base and oil base gel, evaluated the probiotic stability in formulation to obtain an optimum formulation, and finally, investigated the antibacterial activities of that against two common hospital-associated multidrug-resistant pathogens, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). Furthermore, the pharmaceutical aspects of the optimum formulation, including stability, homogeneity, spreadability, pH value, conductivity, and rheological behavior, were assessed.The results indicated that the optimum formulation based on glycerol exhibited desirable pharmaceutical properties, including long-term stability, a perfect level of homogeneity, an acceptable range of spreadability with pseudo-plastic thixotropic behavior, and a promising antibacterial potential against MRSA and VRE. Our findings indicate that this novel probiotic formulation could be an excellent candidate to cope with antibiotic-resistant species, representing a hopeful treatment potential for topical applications, particularly in incurable infections. However, further in vivo studies seem warranted to evaluate their bactericidal activity against multi-drug resistant microorganisms.

Rheology of cellulose nanocrystal and nanofibril suspensions

Nanocellulose is a sustainable nanomaterial and a versatile green platform that has attracted increasing attention. Although the wide applications of its aqueous suspensions are closely related to rheology, comprehensive studies of their rheological behavior, especially the yielding behavior, are still limited. Herein, to investigate the relationship between structure and rheological properties, the viscoelasticity, thixotropy and yielding behavior of two commonly used nanocelluloses, rod-shaped cellulose nanocrystals (CNCs) and filamentous cellulose nanofibrils (CNFs), were systematically investigated. The viscosity, viscoelasticity and thixotropic behavior of the suspensions were analyzed by steady-state shear, frequency sweep, creep-recovery, hysteresis loop, and three-interval thixotropic recovery tests. The yielding behaviors were evaluated through creep, steady-state shear, step shear rate, stress ramps, amplitude sweep, and large amplitude oscillatory shear tests. The rheological properties of the two typical suspensions showed a strong dependence on concentration and time. However, compared to CNC suspensions, CNF suspensions exhibited stronger thixotropy and higher yield stress due to the higher aspect ratio of CNF and the stronger structural skeleton of the suspensions as supported by Simha's equation and micromorphology analysis. This work provides a theoretical rheology basis for the practical applications of nanocellulose suspensions in various fields.

Rheological Properties and Thixotropic Behavior of Cementitious Systems Containing Different Fiber Types

Rheological Properties and Thixotropic Behavior of Cementitious Systems Containing Different Fiber Types

Effect of Urea Usage Rate on Thixotropic Behavior of Cementitious Systems

Effect of Urea Usage Rate on Thixotropic Behavior of Cementitious Systems

3D-printed recycled plastic eco-aggregate (Resin8) concrete

Plastic waste is a global environmental issue, while natural resources, such as sand, is limited and are depleting as opposed to the abundance of waste plastics. This study investigates the suitability of adding recycled plastic waste, in the form of Resin8, for the first time, into 3D printed concrete (3DPC) as fine aggregate replacement. Replacement values of 5 %, 10 % and 15 % of natural sand by volume are investigated, which are further characterised by varying Resin8 particle sizes. Particle sizes of Resin8 included are sub-5 mm, sub-1 mm and a combination of the two at equal proportions (50/50). The Resin8 replacement mixes are tested against the standard ‘reference’ 3DPC mix of Stellenbosch University. A total of ten mixes were formulated, which were 3D printed and cast, to investigate the effect of Resin8 on the printed samples process. The fresh and hardened properties of each mix were investigated, which included slump flow, rheological characterisation, density and air content, buildability, and flexural and compressive strength in two orientations due to the anisotropic nature of 3DPC. Further, the microstructure of samples was investigated using micro-computed tomography and scanning electron microscopy analyses. The addition of Resin8 led to more flowable mixes with less thixotropic behaviour, which decreased the buildability performance. The flexural and compressive strength decreased as the amount of Resin8 increased, while an improved interlayer bond strength was found with the addition of Resin8. An overall performance loss was found by adding Resin8 into 3DPC mixes. However, replacing a portion of fine aggregates in 3D printable concrete with Resin8 is a viable solution that can effectively reduce plastic waste in our environment. Even small amounts of Resin8 replacement can make a significant impact, considering concrete is the most widely used construction material.

Development and characterization of 3D bioprintable and mechanically reinforced hydrogel based on gellan gum/methylcellulose/cellulose nanocrystals

Abstract3D bioprinting has appeared as a promising technology in the area of tissue engineering. Here, bioinks composed of various concentrations of gellan gum (GG), methylcellulose (MC) and cellulose nanocrystal (CNC) were developed for extrusion‐based bioprinting. Among the binary mixtures of GG/MC, the blend of 1% w/w GG and 4% w/w MC (1GG/4MC) provides the best property to further tailoring as bioink. For the ternary mixtures of GG/MC/CNC, 1GG/4MC/4% w/w CNC (1GG/4MC/4CNC) provide the best printability characteristic but not sufficient mechanical performance. Ionic crosslinking using various concentrations of salts including CaCl2, KCl and NaCl were applied to improve the mechanical strength. Both 1GG/4MC/4CNC/0.022% w/w CaCl2 (1GG/4MC/4CNC/0.022CaCl2) and 1GG/4MC/4CNC/0.075% w/w KCl (1GG/4MC/4CNC/0.075KCl) exhibit mechanical stability with good printability. Both provide higher compressive modulus than 1GG/4MC/4CNC and 1GG/4MC, and show great shear‐thinning and thixotropic behaviors. They show porous microstructure and sufficient swelling ratio to maintain high cell viability. Excellent biocompatibility of 1GG/4MC/4CNC/0.022CaCl2 and 1GG/4MC/4CNC/0.075KCl is demonstrated with cell viability of 119.55% and 100.77%, respectively, based on MTT assay. A good cell viability of 97%–98% up to 14 days was attained for both bioprinted constructs. Taken together, these novel 1GG/4MC/4CNC/0.022CaCl2 and 1GG/4MC/4CNC/0.075KCl hydrogels exhibit good attributes for a promising 3D bioprinting material.

Phosphorous slag-based geopolymer cement incorporate with mullite for 3D printing application

In successful 3D printing, the primary key is the proper binder and correct formulation, which leads to the printable mortar. In this work an attempt has been made to fabricate a 3D printable phosphorous slag-based geopolymer concrete with the incorporation of mullite and precisely determined liquid-based activator. The results showed that with the increase of Si/Na from 0.2 to 0.6 increases initial setting time and open time. Presence of mullite resulted in more orientation of Al(IV)-O vibration band in the produced geopolymer matrix so that the maximum compressive strength has achieved in the sample incorporated with mullite and with Si/Na of 0.4 in the activator. The designed geopolymer paste is following the Herschel-Buckley model and show thixotropic behavior, which is useful rheological property for 3D printing applications especially for continuous extrusion and having a desirable layer-by-layer printing.

Rheology of liquid foods under shear flow conditions: Recently used models.

Proper modeling of flow or viscosity curves as a function of shear rate is a useful tool in any engineering activity. The rheology of foods depends on the composition, processing to which they have been subjected and the state of dispersion in which they are found. Liquid foods are complex biosystems, that show non-Newtonian behavior under flow conditions. This review presents models used in recent decades to describe the experimental rheological behavior of various liquid foods, ranging from Newtonian fluids to the most complex. Some non-Newtonian parameters such as those of the Ostwald-de Waele, Bingham, Herschel-Bulkley, Casson, Cross, and Carreau models are summarized. Examples of thixotropic behavior described by the Weltman and Abu-Jdayil models are also presented. In each model, explanations based on the composition and dispersion state of the food are made. This is useful in innovative processing technologies and for scientists new to the field of food rheology. An attempt is made to exemplify and group the expected behavior for most fluid foods, including some for a dysphagia diet, depending on their composition or the dispersed system formed, which will be useful for professionals who wish to compare reported rheological parameters with those obtained experimentally.

Effects of Heating Rates on Microstructural Evolution of Hot Extruded 7075 Aluminum Alloy in the Semi-Solid State and Thixotropic Deformation Behavior.

The non-dendritic microstructure plays a crucial role in determining the rheological properties of semi-solid alloys, which are of the utmost importance for the successful industrial application of the thixoforging process. To further understand the impact of the reheating process on the evolution of microstructure and thixotropic deformation behavior in the semi-solid state, a hot extruded and T6 treated 7075 aluminum alloy was reheated to the selected temperature ranges using varying heating rates. Subsequently, thixo-compression tests were performed. The study found that during reheating and isothermal holding, the elongated microstructure of the as-supplied alloy can transform into equiaxed or spherical grains. The presence of recrystallized grains was found to be closely linked to the penetration of the liquid phase into the recrystallized grain boundaries. Furthermore, it was observed that higher heating rates resulted in smaller grain sizes. The thixotropic flow behavior of the alloy with various microstructures was analyzed using the true stress-strain curves obtained by thixo-compression experiments, which exhibited three stages: a rapid increase in true stress to a peak value, followed by a decrease in true stress and a steady stress until the end of compression. The stress fluctuated with strain during the formation of the slurry at a strain rate of 10 s-1, indicating the significant role of strain rate in material flow during semisolid formation.

Development of Thixotropic Molecular Oleogels Comprising Alkylanilide Gelators by Using a Mixing Strategy.

Molecular oleogels have the potential to be used as materials in healthcare applications. However, their design and synthesis are complex, thus requiring simple and effective methods for their preparation. This paper reports on alkylanilides that are low molecular-weight organogelators, which when appropriately mixed with different alkyl chain lengths could result in the formation of mixed molecular gels that exhibit excellent gel-forming ability and mechanical properties. In addition, the single and mixed molecular organogel systems were found to be applicable as single and mixed molecular oleogel systems capable of gelling oils such as olive oil and squalane. This has been found to be true, especially in molecular oleogel systems consisting of squalane, which is used as solvents in healthcare. The mixed squalene-molecular oleogel systems showed an increase in the critical (minimum) gelation concentration from 1.0 to 0.1 wt.% in the single system and an improvement in the thixotropic behavior recovery time. The thixotropic behavior of the molecular oleogels in the mixed system was quantitatively evaluated through dynamic viscoelasticity measurements; however, it was not observed for the single-system molecular oleogels. Scanning electron microscopy of the xerogels suggested that this behavior is related to the qualitative improvement of the network owing to the refinement of the mesh structure. These mixed molecular oleogels, composed of alkylanilides displaying such thixotropic behavior, could be used as candidates for ointment-base materials in the healthcare field.

Steady and transient rheological properties of four polysaccharides with different chain conformations

AbstractCarbohydrate polymers have broad application prospects, especially in food and cosmetic fields, and rheology is very important for controlling the quality and functions of their final products. Therefore, the steady and transient rheological behaviors of polysaccharides with different chain conformations of triple helix, double helix, and random coils were studied systematically. In our findings, the extraordinary low‐shear thickening phenomena of polysaccharides (lentinan, curdlan, and xanthan) with helix conformation were observed at a certain concentration depending on the stiffness and molecular weight, different from the steady‐shear rheological property of pullulan, which was attributable to the arrangement from order to disorder of stiff chains at the shear rate of < 0.1 s−1. Lentinan, curdlan, and xanthan in solution showed obvious viscoelasticity and thixotropic behavior with significant concentration and stiffness dependence, while the flexible pullulan only exhibited Newtonian viscous fluid even at high concentration of 20%. Stress overshoot for the four polysaccharides occurred after shearing, and the higher stiffness and molecular weight delayed the occurrence of stress overshoot. Obviously, chain conformation plays a key role on controlling the rheology of polysaccharides. This work provides scientific basis for the application of these polysaccharides in food and cosmetics field.

Effect of waste binder material usage rate on thixotropic behaviour of cementitious systems

In order to investigate the feasibility of using waste as an alternative binder in cement-based materials, the effects of using recycled concrete powder (RCP), glass powder (GP), marble powder (MP), and limestone powder (LP) in place of portland cement on the rheological and fresh characteristics of cementitious systems were determined. In this regard, the influence of the utilization of waste materials and the substitution ratio (25% and 35%) on the parameters of the cement paste mixtures that change over time, such as setting time, Marsh-funnel flow time, mini-slump value, viscosity, and dynamic yield stress (DYS), were determined. The effect of 4 different type waste powder materials on the rheology and thixotropy of cementitious systems was investigated using two different methods (loop and constant shear strain rate methods). In order to reduce cement consumption, the effect of the use of waste powder materials on the time-dependent behavior of cementitious systems has been examined, and important results have been obtained for cases (such as producing 3D concrete or self compacting concrete) where time-dependent consistency change is important. It was determined that replacing RCP and GP enhanced the DYS values while replacing MP and LP decreased them. In this context, it was understood that regardless of time, MP and LP promote flowability, whereas RCP and GP diminish flowability. RCP35 had the greatest Ithix_shr and Ithix_vis values at the 20th minute, whereas MP and LP-containing mixtures had the lowest values. The mixtures with the highest and lowest thixotropic degrees were RCP35 and LP35, respectively.

Creation of Polymer Hydrogelator/Poly(Vinyl Alcohol) Composite Molecular Hydrogel Materials.

Polymer hydrogels, including molecular hydrogels, are expected to become materials for healthcare and medical applications, but there is a need to create new functional molecular gels that can meet the required performance. In this paper, for creating new molecular hydrogel materials, the gel formation behavior and its rheological properties for the molecular gels composed of a polymer hydrogelator, poly(3-sodium sulfo-p-phenylene-terephthalamide) polymer (NaPPDT), and water-soluble polymer with the polar group, poly(vinyl alcohol) (PVA) in various concentrations were examined. Molecular hydrogel composites formed from simple mixtures of NaPPDT aqueous solutions (0.1 wt.%~1.0 wt.%) and PVA aqueous solutions exhibited thixotropic behavior in the relatively low concentration region (0.1 wt.%~1.0 wt.%) and spinnable gel formation in the dense concentration region (4.0 wt.%~8.0 wt.%) with 1.0 wt.% NaPPDT aq., showing a characteristic concentration dependence of mechanical behavior. In contrast, each single-component aqueous solution showed no such gel formation in the concentration range in the present experiments. No gel formation behavior was also observed when mixed with common anionic polymers other than NaPPDT. This improvement in gel-forming ability due to mixing may be due to the increased density of the gel's network structure composed of hydrogelator and PVA and rigidity owing to NaPPDT.

Fermented camel milk influenced by soy extract: Apparent viscosity, viscoelastic properties, thixotropic behavior, and biological activities

During fermentation, camel milk forms a fragile, acid-induced gel, which is less stable compared with the gel formed by bovine milk. In this study, camel milk was supplemented with different levels of soy extract, and the obtained blends were fermented with 2 different starter culture strains (a high acidic culture and a low acidic culture). The camel milk-soy extract yogurt treatments were evaluated for pH value, acidity, total phenolic compounds, antioxidant capacities, degree of hydrolysis, α-amylase and α-glucosidase inhibition, angiotensin-converting enzyme inhibition, antiproliferative activities, and rheological properties after 1 and 21 d of storage at 4°C. The results revealed that some of the investigated parameters were significantly affected by the starter culture strain and storage period. For instance, the effect of starter cultures was evident for the degree of hydrolysis, antioxidant capacities, proliferation inhibition, and rheological properties because these treatments led to different responses. Furthermore, the characteristics of camel milk-soy extract yogurt were also influenced by the supplementation level of soy extract, particularly after 21 d of storage. This study could provide valuable knowledge to the dairy industry because it highlighted the characteristics of camel milk-soy yogurt prepared with 2 different starter culture strains.

Investigating the thixotropic behaviour of Tremie Concrete using the Slump-flow test and the Material Point Method

This paper presents a new thixotropic model integrating the Papanastasiou–Bingham model with thixotropy equations to simulate the flow behaviour of Tremie Concrete in the Material Point Method framework. This study investigates the effect of thixotropy on the rheological behaviour of fresh concrete by comparing field measurements with numerical simulations. The comparison yields new insights into a critical and often overlooked behaviour of concrete. A parametric study is performed to understand the effect of model parameters and rest-time on the shear stress response of fresh concrete.

Linear stability of the thixotropic boundary-layer flow over a flat plate

Linear temporal stability of an ideal thixotropic fluid obeying the Moore model in a flat plate boundary-layer flow is investigated in the present work. The Moore model captures the thixotropic and shear-thinning behaviors; both are controlled by the fluid time scale. Besides being shear-thinning and thixotropic, the Moore model can approximate the bi-viscous Bingham model. This means that the Moore fluid mimics the viscoplastic behavior, too, which is controlled by the inverse of the fluid time scale. This study’s main purpose is to investigate the effect of thixotropy on boundary-layer flow stability. However, it is found that without emphasizing the Moore fluid shear-thinning and viscoplastic behaviors, the interpretation of stability results is impossible. Following the Blasius solution, the generalized Blasius equation is derived and solved numerically. Basic solution results show that the Deborah number (the dimensionless fluid time scale) and viscosity-gap ratio reduce the basic flow’s drag force and boundary-layer thickness. Linear stability analysis is used to investigate the flow stability, infinitesimally-small normal-mode perturbations are introduced to the basic flow, and the generalized Orr–Sommerfeld equation is derived, which is solved using the spectral method. Based on the stability results, the thixotropy destabilizes the flow when the Deborah number is large enough. For small values of Deborah number, the shear-thinning and viscoplastic behaviors, which are known to have a stabilizing effect, are dominant and stabilize the flow. As the Deborah number becomes larger, the thixotropy overcomes the stabilizing effect of the shear-thinning and viscoplasticity and destabilizes the flow.

Simulation of circular pipe flow of thixotropic cemented tailings pastes

Cemented tailings pastes (CTPs) exhibit complex thixotropic behaviors, which considerably affect the accurate prediction of pressure drop in circular pipe transport. In this work, the thixotropy of CTPs is incorporated into the numerical simulation via a constitutive thixotropic model. The analytical solution of the velocity profile across the pipe based on the equilibrium rheological model is presented. Comparisons indicate that the Bingham model cannot accurately characterize the flow behaviors of CTPs. It also overestimates the pressure drop in the circular pipe. Moreover, the pressure drop predicted by the novel equilibrium model is overestimated because of thixotropy. A peak of the structural parameter can be observed near the edge of the plug region, which highly influences shear rate distribution. The effects of solids content and flow rate on pressure drop are analyzed. In summary, thixotropy should be considered in the circular pipe flow simulation of CTPs.

Rheological study of highly concentrated aqueous graphene oxide suspensions: the effects of concentration, particle lateral dimensions and number of layers per particle

Aqueous graphene oxide (GO) suspensions have attracted considerable attention due to their unique properties, which can find numerous applications in various fields, from industry to biomedicine. When designing a GO hydrogel for a specific application, a thorough understanding of the effects of appropriate starting material properties and its concentration range on the suspension stability, structural and rheological properties is of essential importance. The present work is concerned with high solids content (from 1.00 to 2.00 w/v%) GO aqueous suspensions exhibiting marked elastic properties. The effects of the GO particles lateral dimensions and the number of GO layers per particle on the flow and viscoelastic properties are investigated. Rheological parameters useful for quantitative interpretation of the results were obtained by fitting the experimental data using Cross, Herschel-Bulkley, and generalized Maxwell models. All GO suspensions showed a marked shear thinning and thixotropic behaviour with a significant yield stress. Their mechanical spectra confirmed viscoelastic behaviour typical for a suspension in an arrested state. Observed differences in values of rheological parameters and their variations with concentration are explained by particle properties and corresponding rotational restrictions, electrostatic attraction/repulsion, nematic phase formation, and particle agglomeration. The research presents fundamental insights into the rheological properties of GO suspensions, which can be manipulated by varying particle geometry and concentration.

Semi-solid thixotropic behavior and microstructure evolution of cold deformed CoCrCu1.2FeNi high-entropy alloy

Semi-solid thixotropic behavior and microstructure evolution of cold deformed CoCrCu1.2FeNi high-entropy alloy

Thixotropy of fresh cement pastes in presence of cationic polymer

Cationic polymer can effectively improve the clay tolerance of polycarboxylate superplasticizer in cement pastes, but the thixotropy of fresh cement pastes in presence of cationic polymer has not received sufficient attention. In this paper, the effect of cationic polymer on the thixotropy of fresh cement pastes containing Na-bentonite was studied. The hydration heat was considered and measured. Besides hysteresis loop areas, the destruction and reconstruction of flocs in thixotropic behaviors of cement pastes were also investigated. The results showed that the cationic polymer delayed the release of cement hydration and decreased the total hydration heat. Cement hydration improved the thixotropy of cement pastes. An obvious decrease of hysteresis loop areas of cement pastes was observed with the addition of cationic polymer, which indicated the decrease of the thixotropy. The equilibrium shear stress, characteristic time of destruction of flocs and incipient structural parameter in thixotropic behaviors were also decreased with the addition of cationic polymer. On the other hand, cationic polymer increased the reconstruction rate of flocculated structure in cement pastes.